I just think the concept of using one's own abilities to generate other abilities to be really cool and something we don't have in league. Something else I think we should have is a copycat champion who's ult does x amount of damage and if the ult kills, you can use one of their basic abilities for a short period of time.
Look at the Morrigan in Smite, her ult lets you copy a champion, be it ally or enemy, with all their abilities including ultimate for a short period of time. LoL doesn't have anything like that, that's a unique champion.
I have a champ concept that can possess enemy bodies, but he mostly just gets stat buffs from it and can't use their abilities.
I think Invoker would be far too complicated and hard to balance. Not because of his abilities, but because a good Invoker would be OP as fuck and a shit one would be shit.
